TUESDAY, Jan. 16, 2018 (HealthDay News) -- It's often said breast-feeding is best for babies, but new research suggests it also might have a significant long-term benefit for moms -- preventing type 2 diabetes.

"We found that a longer duration of breast-feeding was associated with a substantially lower risk of type 2 diabetes in women," said lead study author Erica Gunderson.

In fact, women who breast-fed more than six months had about half the risk for type 2 diabetes as did women who never breast-fed, according to Gunderson. She is an epidemiologist and senior research scientist with Kaiser Permanente Northern California's division of research in Oakland.

In babies, breast-feeding has been linked to a reduced risk for infections, type 1 and type 2 diabetes, some cancers and childhood overweight and obesity. In mothers, breast-feeding helps return to pre-pregnancy weight and decrease postpartum blood loss and menstrual blood loss. Breast-feeding has also been associated with a lower risk for breast and ovarian cancer in mothers, according to the American Academy of Pediatrics.

The new study began 30 years ago when researchers recruited young women, then 18 to 30 years old, for a study on heart disease. During that study, researchers also gathered information on pregnancy and breast-feeding. They also tested the women every five years for diabetes.

That produced information on more than 1,200 women for the new study. Half were black, and half were white. All had at least one live birth.

The researchers adjusted the data to account for other factors that could affect a woman's risk for type 2 diabetes. These included income, education, weight, diet quality, physical activity, medication use and other health conditions.

By the end of the 30-year study, 182 of the women had developed type 2 diabetes.

Women who breast-fed for 6 to 12 months had a 48 percent lower risk for type 2 diabetes than women who never breast-fed, the findings showed.

The protective effect of breast-feeding didn't differ by race or the presence of gestational diabetes, the study found.

Although the study cannot prove a cause-and-effect relationship because it was observational, the researchers suspect that breast-feeding quickly returns the body to a more normal metabolic state. Other studies have shown that when women breast-feed, their triglycerides (a type of blood fat) and blood sugar levels return to normal more quickly. Breast-feeding moms also secrete less insulin and use fat tissue stores.

Dr. Rekha Kumar is an endocrinologist at New York-Presbyterian/Weill Cornell Medical Center's Comprehensive Weight Control Center in New York City. She also thinks that breast-feeding likely has beneficial effects on insulin and blood sugar metabolism.

"Breast-feeding makes you more sensitive to the hormone insulin," Kumar said.

However, she added that larger studies need to be done to duplicate the findings and to better understand the mechanism behind the protective effect.

Still, Kumar said: "I loved this study. For a long time we have talked about the benefits of breast-feeding on infants, but we don't always talk about the long-term benefits for mothers."

Study author Gunderson said the benefits of breast-feeding may go beyond a reduction in type 2 diabetes. Because type 2 diabetes is a very strong risk factor for heart disease, it's possible that breast-feeding could also lead to a reduction in heart disease, which could then potentially reduce health care costs.